The present invention generally relates to an activation apparatus for activating surfaces of articles such as powdery or granular material, etc. through production of physical or chemical reactions on the surfaces of the articles by irradiating, under various gaseous atmospheres and at varied temperatures and pressures, plasma ions onto the articles so as to impart a lipophilic nature, hydrophilic nature and lyophilic nature to the articles or improve dispersion property of the articles and more particularly, to a plasma generator for use in the activation apparatus or the like.